1. Field of the Invention
This invention relates to a rotary head type magnetic tape apparatus which may be advantageously applied to, for example, a digital audio tape recorder.
2. Related Art Statement
A rotary head digital tape recorder (DAT) has been used as a tape recorder capable of performing high density recording of audio signals.
With a DAT, input audio data may be recorded, using a rotary head or heads provided on a rotary drum, on a magnetic tape placed at a predetermined wrapping angle on the drum, or the audio data previously recorded on the magnetic tape may be reproduced using the same magnetic head or heads.
To record or reproduce audio data with a DAT, it is necessary to control the speed with which the recording track on the magnetic tape passes the rotary head or heads. Previously this has been done by detecting the relative speed between the magnetic tape and the rotary head or heads from the frequency of reproduced clock signals contained in the reproduced signals.
With this relative speed controlling method, the reproduced signals obtained upon scanning the magnetic tape are input to a phase locked loop (PLL) type clock reproducing circuit, the relative speed between the magnetic tape and the rotary head or heads is detected on the basis of the frequency of the reproduced clock signals contained in the reproduced signals, and the number of revolutions of the rotary drum is controlled so that this relative speed will be maintained at a constant value.
However, in this type of control method, while the relative speed between the tape and the head may be kept constant during normal recording or reproducing operations, relative speed detection cannot be achieved when the PLL in the clock signal reproducing circuit is not locked and hence the reproduced clock signal cannot be obtained, for example, during starting of the tape or during high-speed search operation.